Article for low-temperature use



Patented May 25, 1954 ARTICLE FOR LOW-TEMPERATURE USE Charles Martin Offenhauer, Lewiston, N. Y., assignor to Union Carbide and Carbon Corporation, a. corporation of New York No Drawing. Application February 8, 1952,

4 Serial No. 270,759

4 Claims. 1

This invention relates to wrought steel articles having superior impact resistance at temperatures below C.

Most steels when cooled below room temperatures become less resistant to shock or impact. The resistance to impact does not ordinarily decrease proportionally with the temperature but decreases precipitously when the steel is cooled below a critical temperature which is referred to as the transition temperature. Machine parts and structural members subjected to impact at low temperatures must be made of steel having a transition temperature lower than their operating temperatures or else compensations must be made in the design of such articles to provide for their greatly diminished resistance to impact.

It is an object of the invention to provide articles for use at sub-zero temperatures which have an increased resistance to impact.

Another object of the invention is to lower the transition temperature of certain steels and thus render articles made from such steels more useful for jobs in which the articles are subjected to impact at low temperatures.

Efforts in the past to improve the low temperature properties of steels have resulted in the discovery that the addition of aluminum to certain steels has a beneficial effect. For example, the addition of aluminum to chromium-nickelcopper steels has been taught for the purpose of lowering the transition temperature of these steels. The present invention is based on the discovery that articles having superior low temperature properties can be fabricated from chromium-nickel-copper steels to which have been added specified percentages of both aluminum and nitrogen. The steels thus obtained have greater resistance to impact and lower transition temperatures than those steels to which aluminum alone is added despite the fact that nitrogen is taught by the art to be an embrittling agent.

' The objects of the invention are accomplished by fabricating articles from steel having the following composition: carbon not to exceed 0.25%, not over 2% manganese, not over 1% silicon, 0.25% to 1.25% copper, not over 5% nickel, 0.25% to 3.25% chromium, 0.08% to 0.3% aluminum, 0.013% to 0.03% nitrogen, balance substantially all iron.

A preferred composition falls within the following range: 0.0l% to 0.2% carbon, 0.2% to 1% manganese, 0.02% to 0.8% silicon, 0.25% to 1.25% copper, 0.5% to 3% nickel, 0.5% to 1.5% chromium, 0.08% to 0.3% aluminum, 0.013% to 0.03% nitrogen balance substantially all iron.

Steels manufactured by conventional methods have a nitrogen content of about 0.007%. The advantages of this invention are not obtained unless the nitrogen content of the steel is above at least 0.013% and unless this higher than normal nitrogen content is coupled with a soluble aluminum content of at least 0.08%. Any proportions of the two materials within the ranges 0.013% to 0.03% for nitrogen and 0.08% to 0.3% for aluminum will impart to the steel from which the articles of the invention are fabricated an improved resistance to impact at low temperatures. It is of interest to note that while a nitrogen content of 0.03% is within the preferred limits of the invention, a nitrogen content of no more than about 0.02% is required to obtain most of the improvements in the low temperature properties of the steel.

Table I sets forth data showing the improvements accomplished by the invention. The tests were conducted on a Charpy machine using standard keyhole specimens. The compositions of the specimens were substantially all iron plus the elements listed in the table. The specimens were cooled by immersion in a petroleum-ether which was cooled by liquid oxygen or nitrogen. After immersion in the cooling fluid for one hour, the test specimens were quickly transferred to a Charpy machine and the hammer of the machine released immediately.

Most of the specimens tested and reported in Table I exhibited a precipitous decrease in resistance to impact when cooled below a certain temperature. The impact resistance of other specimens decreased more gradually within the temperature range used in the tests. For purposes of comparison, an impact value of 15 footpounds, representative of a significant value, was chosen as the reference point. The temperature at which a steel exhibits an impact strength of 15 foot-pounds is designated the transition temperature in the table.

: The proportions of the elements in the steel were varied from one specimen to another to establish more clearly the efiect of the combination of nitrogen and aluminum, within the specifled limits, on the impact strength of the steel. For convenience in making comparisons, the tests results are grouped so that within any group one element in addition to the aluminum and nitrogen is the principal variant. No nitrogen was added intentionally to those alloys containing 0.007% nitrogen, this being the normal nitrogen content of the steels made by conventional methods.

The specimens were also given several different heat treatments. The values appearing in column I of Table I are those obtained with specimens normalized at 925 C. The values in column II are those for specimens normalized at 925 C. and stress relieved at 593 C. The values in: column: III are those for specimens normalizedat 925 C. and stress relieved at The steels from which articles of the invention are fabricated have a normal crystal structure and require no special treatment during fabrication. Welded pressure vessels fabricated from steels according to the invention give excellent service wh'en subjectedtto loW'temperatures during use. Conventional fabricating techniques,

650 C. such as welding, forging, and rolling, can be em- TabZeI CharpyKeyhole Impact Strength (Ft-lb. per Sq. Cm.)

I II III Chemical Oompositin-Per Cent Element Varied Test Test s' Temp., Temp.,

' Transition 0. Transition 0. Transition Temp., Temp., 0. Temp., O.

C Mn Si Cu Ni 0! Al N 160 183 196 160 183 160 183 0.045 0. 23 0. l1 0. 51 1.45 0. 92 0.18 0. 007 46. 0 5. 0 13. 5 4.1 Above -l60 5. 7 3. 0 Above 160. Carbon 0. 052 0. 27 Ol 13 0. 51 1; 48 0. 9S 0. 16 0. 018 55'. 0 8. 0 52. 0 5. 2 170 49. 5 3. 8 170.

0.14 0.520.260.4411441.010.150.007 32.8 f 3.6 5.4 7.1 0. 17. 0. 50 0. 27 0. 531.47 1. 00 0. 0.018 26. 2 11. 8 5. 5 9. 0 0. 045 0.27 0.12 1. 06 1. 45 0. 97 0.15 0.007 48. 0 6. 3 5. 8 4. 0 2. 8 Above '-160. Manganese. 0. 047 0. 2S 0. 17 l. 011. 50 1. 00 0.17 01018 43.0 4. 7 4.2 3. 4 170.

0. 047 0. 78 0191.08 1. 431. 01 0. 26 0. 018 20. 0 7. 0 18. 2 4. 2 0. 048 0. 29 0. 15 0.53 l. 96 1. 00 0.26 0. 007 33. 5 4. 2 34. 5 5.1 0 3. 4 Above 160. Silicon 0. 046 0. 22 0.11 0. 511. 50 0. 91 0. 17 0. 016 76. 0 55. 5 8. 8 .0 5.3 1701 0. 085 0.42 0.29 0.93 1.40 0. 71 0. 09 0.015 23. 0 19.0 Below l83 0. 048 0.29 0.15 0.53 1. 961. 00 0. 26 0. 007 33. 5 4. 2 34. 5 5. 1 5. O 3. 4 Above 160. Copper 0. 040 0.22 0. 11 0. 51 1. 50 0. 91 0.17 0. 016 76. 0 55. 5 8. 8 "0 70. 0 5.3 70.

0 045 0. 27 0. 12 l. 061. 45 0. 97 0.15 0. 007 48. 0 6. 3 5. 8 4. 0 Above 160-" 6. 5 2. 8 .Above 160. 0 038 0.30 0.09 1.09 1.44090 0.23 0.021 48.5 31.0 17.5 3.0 0 0.045 0.27 0.12 1.06 1.45 0.97 0.15 0.007 48.0 6.3 0 5.8 4.0 6 5 8 Above 160. Nickel 0. 033 0. 30 0. 091. 00 1. 44 0. 96 0. 23 0. 021 48. 5 31. O Below --l83 17. 5 3.0

0. 075 0. 44 0. 31 0. 50 2. 63 0.77 0. 21 0. 007 16. 0 3. 4 16 0. 032 0.26 0. 13 0.50 2.161. 00 0.1-3 0. 021 90. 0 5. 5 Q 0. 088 0. 4S 0. 33 0. 501. 51 0. 76 0. 20 0. 007 54. 0 11. 4 chromlmnnn 0.085 0. 42 O. 29 0. 931. 0. 71 0. 09 0. 015 H-.. 23. 0 .3

0. 14 0. 52 0. 26 0. 441. 441. 01 0. 15 0. 007 32.8 3. 6 0.13 0.42023 0.551.60 1.050115 0.019 16.0 0.088 0. 48 0.33 0. 501. 51 0.76 0.20 0. 007 54. 0 11.4 Aluminumz... 0. 085 0. 42 0. 29 0.93 1. 40 0. 71 0. 09 0. 015 23. 0

0. 094 0. 54 0.25 0. 53 1. 60 0. 87 0.26 0. 007 9. 7 5. 0 Above 150..- O. 10 0. 59 O. 27 0.52 1. 55 0. 78 0. 23 0. 018 31. 2 9. 0 170 1 Test-temp, 150C.'

Carbon is theprincipal element, besides nitrogen, that is varied in four of the specimens tested. The data obtained from the testin of these specimens are recorded on successive lines in the table. These data indicate that those specimens having a highinitrogen content of 0.018% and an aluminum content. above the specified minimum of 0.08% are generally more resistant to impact and have lower transition temperatures than those specimens having a normal nitrogen content of 0.007%. This relationship holds true whether the carbon content of the specimen, is in the relatively low range of 0.045% to 0.052% orv in the higher range of 0.14% to 0.17%.

In theothergroups of specimens in the table eithermanganese, silicon, copper, nickel, chromium, or aluminum is, the principal element varied besides. nitrogen. The data for these groups show results similar to those for the group in which carbon and nitrogen are the principal elements varied. In each group, those specimens having a nitrogen and aluminum content within the specified limits exhibited improved low temperature impact resistance. The presenceof a high aluminum content in a specimen. does not impart to that specimen the advantages of the invention- In this respect the last group in the table in whichaluminum and nitrogen are the principal elements varied is of interest. Those specimens having both a high nitrogen and aluminum content within the limits of the invention exhibited a substantially lower transition temperature than those specimens having a nitrogen content lower than 0.013 and thus outside-the limits. of. the invention.

ployed in makingthe articles of the.invention.

What is claimed is:

1. An article required to resist impact at tem-. peratures below 0 0., said article beingcomposed ofa wrought steel having a composition comprising, carbon in an amount not to exceed 0.25%, not over 2%. manganese,. not .over 1% silicon, 0.25% to 1.25% copper, notover 5% nickel, 0.25% to 3.25% chromium. 0.08% to. 0.3% aluminum, 0.013% to 0.03% nitrogen,. the remainder iron and incidental impurities, and said steel having. a transition temperature not higher than 'C.

2. .An article required to resist impact at temperatures below 0 'C., said'articles being composed of a wrought steelLhaving a. composition comprising 001% to 0.2% carbon, 0.2% to 1%- manganese, 0.02% to 0.8% silicon, 0.25% to 1.25%. copper, 0.5% to 3% nickel, 0.5% to 1.5% chromium, 0.08% .to 0.3% aluminum, 0.013% to 0.03% nitrogen, the remainder iron and incidental impurities, and said steel having a. transition temperature not higher than 170 C.

3. A welded j pressure vessel for use at temperatures below 0 C., said welded pressure vessel being composed of a wrought steel having a composition comprising carbonin an amount not to exceed 0.25%, not .over.2% manganese, not over 1% silicon, 0.25% to 1.25% copper, not over 5% nickel, 0.25% to 3.25% chromium, 0.08% to 0.3% aluminum, 0.013 to 0.03 nitrogen, the remainder iron and incidental impurities, and said steel having a transitiontemperature not higher than-170 C.

4. A welded, pressure" vessel. for. use at term peratures below 0 C., said welded pressure vessel being composed of a wrought steel having a composition comprising 0.01% to 0.2% carbon, 0.2% to 1% manganese, 0.02% to 0.8% silicon, 0.25% to 1.25% copper, 0.5% to 3% nickel, 0.5% to 1.5% chromium, 0.08% to 0.3% aluminum, 0.013% to 0.03% nitrogen, the remainder iron and incidental impurities, and said steel having a transition temperature not higher than 170 C.

References Cited in the file of this patent UNITED STATES PATENTS Number Q OTHER REFERENCE Transactions, American Institute of Mining and Metallurgical Engineers, vol. 125, page 570. Published in 1937 by the A. I, M. E., New York.

Mechanical Properties of Metals at Low Temperatures, pages 50 to 55. Published in 1952 by the U. S. Government Printing Ofiice, Washington, D. C. 

2. AN ARTICLE REQUIRED TO RESIST IMPACT AT TEMPERATURE BELOW 0* C., SAID ARTICLES BEING COMPOSED OF A WROUGHT STEEL HAVING A COMPOSITION MANGANESE, 0.01% TO 0.2% CARBON, 0.2% TO 1% MANGANESE, 0.02% TO 0.8% SILICON, 0.25% TO 1.25% COPPER, 0.5% TO 3% NICKEL, 0.5% TO 1.5% CHROMIUM, 0.08% TO 0.3% ALUMINUM, 0.013% TO 0.03% NITROGEN, THE REMAINDER IRON AND INCIDENTAL IMPURITIES, AND SAID STEEL HAVING A TRANSITION TEMPERATURE NOT HIGHER THAN -170* C. 